• Energy Research

Dans cette étude, nous avons quantifié la sensibilité de la neige au réchauffement climatique dans certains sites de montagne ayant un climat méditerranéen, notamment les Pyrénées en Espagne et en Andorre, la Sierra Nevada en Espagne et en Californie (États-Unis), l'Atlas au Maroc et les Andes au Chili. Les observations météorologiques à haute altitude ont été utilisées pour simuler le bilan énergétique et massique de la neige (SEMB) et calculer sa sensibilité au climat. Des sensibilités climatiques très différentes étaient évidentes entre les différents sites. Par exemple, des réductions de 9% à 19% et de 6 à 28 jours de l'équivalent moyen en eau de la neige (SWE) et de la durée de la neige, respectivement, ont été trouvées par augmentation de °C. Les changements simulés dans les précipitations (±20%) n'ont pas affecté les sensibilités. Les Andes et les montagnes de l'Atlas ont un manteau neigeux peu profond et froid, et le rayonnement net domine le SEMB ; et explique leur sensibilité relativement faible au réchauffement climatique. Les Pyrénées et la Sierra Nevada aux États-Unis ont un manteau neigeux plus profond et plus chaud, et le flux de chaleur sensible est plus important dans le SEMB ; cela explique les sensibilités beaucoup plus grandes de ces régions. Les différences de sensibilité aident à expliquer pourquoi, dans les régions où les modèles climatiques prévoient des augmentations de température relativement plus importantes et des conditions plus sèches d'ici 2050 (comme la Sierra Nevada espagnole et les montagnes de l'Atlas marocain), le déclin de l'accumulation et de la durée de la neige est similaire à d'autres sites (comme les Pyrénées et la Sierra Nevada américaine), où les modèles prévoient des précipitations stables et un réchauffement plus atténué. Le manteau neigeux dans les Andes (Chili) présentait la plus faible sensibilité au réchauffement et ne devrait subir que des changements modérés (une diminution de <12 % du SWE moyen et une réduction de < 7 jours de la durée de la neige sous RCP 4.5). L'accumulation et la durée de la neige dans les autres régions devraient diminuer considérablement (un minimum de 40 % de SWE moyen et 15 jours de durée de la neige) d'ici 2050. En este estudio cuantificamos la sensibilidad de la nieve al calentamiento climático en sitios de montaña seleccionados que tienen un clima mediterráneo, incluidos los Pirineos en España y Andorra, la Sierra Nevada en España y California (EE. UU.), el Atlas en Marruecos y los Andes en Chile. Se utilizaron datos meteorológicos de altitudes elevadas para simular el balance de energía y masa de la nieve (SEMB) y calcular su sensibilidad al clima. Se evidenciaron sensibilidades climáticas muy diferentes entre los distintos sitios. Por ejemplo, se encontraron reducciones de 9%–19% y 6–28 días en el equivalente medio de agua de nieve (SWE) y la duración de la nieve, respectivamente, por aumento de °C. Los cambios simulados en la precipitación (±20%) no afectaron las sensibilidades. Los Andes y las montañas del Atlas tienen una capa de nieve poco profunda y fría, y la radiación neta domina el SEMB; y explica su sensibilidad relativamente baja al calentamiento climático. Los Pirineos y EE.UU. Sierra Nevada tienen una capa de nieve más profunda y cálida, y el flujo de calor sensible es más importante en el SEMB; esto explica las sensibilidades mucho mayores de estas regiones. Las diferencias en la sensibilidad ayudan a explicar por qué, en regiones donde los modelos climáticos proyectan aumentos de temperatura relativamente mayores y condiciones más secas para 2050 (como la Sierra Nevada española y las montañas del Atlas marroquí), la disminución en la acumulación y duración de la nieve es similar a otros sitios (como los Pirineos y la Sierra Nevada de EE. UU.), donde los modelos proyectan precipitaciones estables y un calentamiento más atenuado. La capa de nieve en los Andes (Chile) exhibió la menor sensibilidad al calentamiento y se espera que experimente solo un cambio moderado (una disminución de <12% en el SWE medio y una reducción de < 7 días en la duración de la nieve por debajo de RCP 4.5). Se prevé que la acumulación y la duración de la nieve en las otras regiones disminuyan sustancialmente (un mínimo del 40% en el SWE medio y 15 días en la duración de la nieve) para 2050. In this study we quantified the sensitivity of snow to climate warming in selected mountain sites having a Mediterranean climate, including the Pyrenees in Spain and Andorra, the Sierra Nevada in Spain and California (USA), the Atlas in Morocco, and the Andes in Chile. Meteorological observations from high elevations were used to simulate the snow energy and mass balance (SEMB) and calculate its sensitivity to climate. Very different climate sensitivities were evident amongst the various sites. For example, reductions of 9%–19% and 6–28 days in the mean snow water equivalent (SWE) and snow duration, respectively, were found per °C increase. Simulated changes in precipitation (±20%) did not affect the sensitivities. The Andes and Atlas Mountains have a shallow and cold snowpack, and net radiation dominates the SEMB; and explains their relatively low sensitivity to climate warming. The Pyrenees and USA Sierra Nevada have a deeper and warmer snowpack, and sensible heat flux is more important in the SEMB; this explains the much greater sensitivities of these regions. Differences in sensitivity help explain why, in regions where climate models project relatively greater temperature increases and drier conditions by 2050 (such as the Spanish Sierra Nevada and the Moroccan Atlas Mountains), the decline in snow accumulation and duration is similar to other sites (such as the Pyrenees and the USA Sierra Nevada), where models project stable precipitation and more attenuated warming. The snowpack in the Andes (Chile) exhibited the lowest sensitivity to warming, and is expected to undergo only moderate change (a decrease of <12% in mean SWE, and a reduction of < 7 days in snow duration under RCP 4.5). Snow accumulation and duration in the other regions are projected to decrease substantially (a minimum of 40% in mean SWE and 15 days in snow duration) by 2050. في هذه الدراسة، قمنا بقياس حساسية الثلوج للاحترار المناخي في مواقع جبلية مختارة ذات مناخ متوسطي، بما في ذلك جبال البرانس في إسبانيا وأندورا، وسييرا نيفادا في إسبانيا وكاليفورنيا (الولايات المتحدة الأمريكية)، والأطلس في المغرب، والأنديز في تشيلي. تم استخدام ملاحظات الأرصاد الجوية من الارتفاعات العالية لمحاكاة طاقة الثلج وتوازن الكتلة (SEMB) وحساب حساسيتها للمناخ. كانت الحساسيات المناخية المختلفة واضحة بين المواقع المختلفة. على سبيل المثال، تم العثور على انخفاضات بنسبة 9٪ -19 ٪ و 6–28 يومًا في متوسط مكافئ مياه الثلج (SWE) ومدة الثلوج، على التوالي، لكل زيادة درجة مئوية. لم تؤثر التغيرات المحاكاة في هطول الأمطار (±20 ٪) على الحساسيات. تحتوي جبال الأنديز والأطلس على كتلة ثلجية ضحلة وباردة، ويهيمن الإشعاع الصافي على SEMB ؛ ويفسر حساسيتها المنخفضة نسبيًا للاحترار المناخي. تتمتع جبال البرانس وسييرا نيفادا الأمريكية بغطاء ثلجي أعمق وأكثر دفئًا، ويعد التدفق الحراري المعقول أكثر أهمية في SEMB ؛ وهذا ما يفسر الحساسيات الأكبر بكثير لهذه المناطق. تساعد الاختلافات في الحساسية في تفسير السبب، في المناطق التي تتوقع فيها النماذج المناخية زيادات أكبر نسبيًا في درجات الحرارة وظروف أكثر جفافًا بحلول عام 2050 (مثل سييرا نيفادا الإسبانية وجبال الأطلس المغربية)، فإن الانخفاض في تراكم الثلوج ومدتها مشابه للمواقع الأخرى (مثل جبال البرانس وسييرا نيفادا الأمريكية)، حيث تتوقع النماذج هطول الأمطار المستقر والاحترار الأكثر توهينًا. أظهرت الكتلة الثلجية في جبال الأنديز (تشيلي) أدنى حساسية للاحترار، ومن المتوقع أن تخضع فقط لتغيير معتدل (انخفاض بنسبة <12 ٪ في متوسط SWE، وانخفاض بنسبة < 7 أيام في مدة الثلوج بموجب RCP 4.5). من المتوقع أن ينخفض تراكم الثلوج ومدتها في المناطق الأخرى بشكل كبير (بحد أدنى 40 ٪ في متوسط SWE و 15 يومًا في مدة الثلوج) بحلول عام 2050.

ABSTRACTThis study analyses variability and trends of atmospheric evaporative demand (AED) across Uruguay in the past four decades. Changes were assessed using pan evaporation measurements from 10 meteorological stations and compared to PenPan model calculations, which is a physically based model that employs meteorological data as input. Results demonstrate a high agreement between the observed AED and those estimated from the PenPan model. Both observations and model estimations agree on a high interannual variability in AED, though being statistically insignificant (p > 0.05) at seasonal and annual scales. Given that AED shows high sensitivity to changes in relative humidity and sunshine duration, as a surrogate of solar radiation, the lack of significant trends in the AED observations and estimations over Uruguay can be linked to the insignificant trend found for these climate variables for the period from 1973 to 2014. This is the first study that reports Pan evaporation trends for this part of the world, helping to infill gaps for mid‐latitude Southern Hemisphere areas, which are poorly represented in Pan evaporation trends.

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella–Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were used to simulate reservoir inflow using the Regional Hydro-Ecologic Simulation System (RHESsys) and to analyze the future impacts on water management (2021–2050). Results reveal a clear decrease in dam inflow (−34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (−31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir’s inflows, different water management strategies are needed to mitigate the effects of the expected climate change.

AbstractAttribution of trends in streamflow is complex, but essential, in identifying optimal management options for water resources. Disagreement remains on the relative role of climate change and human factors, including water abstractions and land cover change, in driving change in annual streamflow. We construct a very dense network of gauging stations (n = 1,874) from Ireland, the United Kingdom, France, Spain, and Portugal for the period of 1961–2012 to detect and then attribute changes in annual streamflow. Using regression‐based techniques, we show that climate (precipitation and atmospheric evaporative demand) explains many of the observed trends in northwest Europe, while for southwest Europe human disturbances better explain both temporal and spatial trends. For the latter, large increases in irrigated areas, agricultural intensification, and natural revegetation of marginal lands are inferred to be the dominant drivers of decreases in streamflow.

42 Pag., 13 Fig. The definitive version is available at: http://www.agu.org/journals/jd/ In this study we analyzed the influence of the El Niño‐Southern Oscillation (ENSO) phenomenon on drought severity at the global scale. A unique aspect of the analysis is that the ENSO influence was quantified using a multiscalar drought indicator, which allowed assessment of the role of the ENSO phases on drought types affecting various hydrological, agricultural and environmental systems. The study was based on ENSO composites corresponding to El Niño and La Niña phases, which were obtained from the winter El Niño 3.4 index for the period 1901–2006. Drought was identified in a multiscalar way using the Standardized Precipitation Evapotranspiration Index (SPEI) and the global SPEIbase data set. The study revealed the differing impacts of the El Niño and La Niña phases on drought severity, the time scales of droughts, and the period of the year when the ENSO phases explained drought variability worldwide. In large areas of America and eastern Europe the role of ENSO events were evident at the shortest time scales (1–3 months) at the beginning of events, but in areas of South Africa, Australia and Southeast Asia the effects were more obvious some months later, and at longer time scales. We also identified areas where severe drought conditions are associated with more than 70% of ENSO events. The persistence of the drought signal at longer time‐scales (e.g., 6‐ or 12‐months) is not directly determined by the atmospheric circulation response to the SST anomalies, since the SPEI anomalies will be caused by the cumulative dry conditions in some specific months. Knowledge of how these effects differ as a function of the El Niño and La Niña phases, and how they propagate throughout the drought time scales could aid in the prediction of the expected drought severity associated with the ENSO. Lags detected during the study may help forecasting of dry conditions in some regions up to one year before their occurrence. This work has been supported by the research projects CGL2008-01189/BTE and CGL2006-11619/HID financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, “Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica” and “La nieve en el Pirineo aragonés: Distribución espacial y su respuesta a las condiciones climáticas” Financed by “Obra Social La Caixa” and the Aragón Government. Peer reviewed

Abstract. The mountain cryosphere of mainland Europe is recognized to have important impacts on a range of environmental processes. In this paper, we provide an overview on the current knowledge on snow, glacier, and permafrost processes, as well as their past, current, and future evolution. We additionally provide an assessment of current cryosphere research in Europe and point to the different domains requiring further research. Emphasis is given to our understanding of climate–cryosphere interactions, cryosphere controls on physical and biological mountain systems, and related impacts. By the end of the century, Europe's mountain cryosphere will have changed to an extent that will impact the landscape, the hydrological regimes, the water resources, and the infrastructure. The impacts will not remain confined to the mountain area but also affect the downstream lowlands, entailing a wide range of socioeconomical consequences. European mountains will have a completely different visual appearance, in which low- and mid-range-altitude glaciers will have disappeared and even large valley glaciers will have experienced significant retreat and mass loss. Due to increased air temperatures and related shifts from solid to liquid precipitation, seasonal snow lines will be found at much higher altitudes, and the snow season will be much shorter than today. These changes in snow and ice melt will cause a shift in the timing of discharge maxima, as well as a transition of runoff regimes from glacial to nival and from nival to pluvial. This will entail significant impacts on the seasonality of high-altitude water availability, with consequences for water storage and management in reservoirs for drinking water, irrigation, and hydropower production. Whereas an upward shift of the tree line and expansion of vegetation can be expected into current periglacial areas, the disappearance of permafrost at lower altitudes and its warming at higher elevations will likely result in mass movements and process chains beyond historical experience. Future cryospheric research has the responsibility not only to foster awareness of these expected changes and to develop targeted strategies to precisely quantify their magnitude and rate of occurrence but also to help in the development of approaches to adapt to these changes and to mitigate their consequences. Major joint efforts are required in the domain of cryospheric monitoring, which will require coordination in terms of data availability and quality. In particular, we recognize the quantification of high-altitude precipitation as a key source of uncertainty in projections of future changes. Improvements in numerical modeling and a better understanding of process chains affecting high-altitude mass movements are the two further fields that – in our view – future cryospheric research should focus on.